The invention is applicable to any audio related applications where audio level variations are a problem.
This invention is solving a problem inherent in AGC amplifiers. An AGC amplifier will achieve maximum gain during periods where there is no signal. This results in a pumping effect as seen from the user. The gain will vary a lot as the signal goes through periods of silence and signal presence.
There are many AGC implementations, both analogue and digital, known today.
U.S. Pat. No. 5,734,974 describes a direct conversion radio receiver comprising a stepwise variable gain control. The output signal (audio) from the detector/low pass filter is fed into an AGC detector. In the AGC detector the signal is integrated to form an AGC signal indicative of the average level of the output signal. A state machine is coupled to the AGC detector and generates a control signal for controlling a stepwise variable gain control circuit. This circuit generates a signal to control the gain of an RF amplifier in the receiver. The state machine introduces a delay (hysteresis function) in the gain control at a raising or falling input signal. However, the output signal is compared against a maximum or minimum allowed level prior to a stepwise gain change as a result of a new state function in the state machine.
Briefly the present invention provides a new and improved AGC amplifier which shows no or little pumping effects. It is very easily implemented, e.g. in a DSP, and is very easily controlled, e.g. as to attack/release levels and times.
This object of the present invention is achieved in a system as defined in the appended claim 1. Further embodiments of the invention appear from the following dependent claims.